1. Field of the Invention
The present invention relates to an ink-jet printhead. More particularly, the present invention relates to an ink-jet printhead having a high nozzle density.
2. Description of the Related Art
Inkjet printing heads are devices for printing in a predetermined color image by ejecting a small droplet of printing ink at a desired position on a recording sheet. Ink ejection mechanisms of an ink-jet printer are generally categorized into two types: an electro-thermal transducer type (bubble-jet type), in which a heat source is employed to form a bubble in ink causing an ink droplet to be ejected, and an electromechanical transducer type, in which a piezoelectric crystal bends to change the volume of ink causing an ink droplet to be expelled.
Referring to FIGS. 1A and 1B, a conventional bubble-jet type ink ejection mechanism will now be described. When a current pulse is applied to a heater 12 consisting of resistive heating elements formed in an ink channel 10 where a nozzle 11 is located, heat generated by the heater 12 boils ink 14 to form a bubble 15 within the ink channel 10, which causes an ink droplet 14xe2x80x2 to be ejected.
There are multiple factors and parameters to consider in making an ink-jet printhead having a bubble-jet type ink ejector. First, it should be simple to manufacture, have a low manufacturing cost, and be capable of being mass-produced. Second, in order to produce high quality color images, the formation of minute, undesirable satellite ink droplets that usually trail an ejected main ink droplet must be avoided. Third, when ink is ejected from one nozzle or when ink refills an ink chamber after ink ejection, cross-talk with adjacent nozzles from which no ink is ejected must also be avoided. To this end, a back flow of ink in a direction opposite to the direction ink is ejected from a nozzle must be prevented during ink ejection. For this purpose, a second heater 13 as shown in FIGS. 1A and 1B is typically provided to prevent a back flow of the ink 14. The second heater 13 generates heat earlier than the first heater 12, which causes a bubble 16 to shut off the ink channel 10 behind the first heater 12. Then, the first heater 12 generates heat, and the bubble 15 expands to cause the ink droplet 14xe2x80x2 to be ejected. Fourth, for high-speed printing, a cycle beginning with ink ejection and ending with ink refill in the ink channel must be carried out in as short a period of time as possible. Fifth, a nozzle and an ink channel for introducing ink to the nozzle must not be clogged by a foreign material or by solidified ink.
The above requirements, however, tend to conflict with one another. Furthermore, the performance of an ink-jet printhead is closely associated with and affected by the structure and design of an ink chamber, an ink channel, and a heater, as well as by the type of formation and expansion of bubbles, and the relative size of each component.
In order to offer higher resolutions and to lower the price of an ink-jet printhead, an area per unit nozzle must be minimized and a nozzle density must be maximized.
In terms of the ink ejection mechanism utilized, conventional bubble-jet type ink-jet printheads are categorized into two types. A first type of printhead shown in FIG. 2 (disclosed in U. S. Pat. No. 5,635,966) is designed to eject an ink droplet in a direction in which a bubble 23 is formed. In this structure, an ink chamber 22 for containing a predetermined amount of ink 25 has an area larger than a nozzle 21. Furthermore, ink feed grooves for supplying the ink 25 to the ink chamber 22 are separated from the nozzle 21, thereby increasing an area per unit nozzle. Thus, the first type of printhead has a limit in increasing nozzle density in the printhead.
A second type of printhead shown in FIG. 3 (disclosed in U. S. Pat. No. 4,296,421) is designed to eject an ink droplet 35 horizontally, that is, in a direction perpendicular to that in which a bubble 33 is formed. Each component in this structure is difficult to arrange vertically due to restriction in the process. Since a nozzle 31 is arranged horizontally, the second type of printhead also involves a limit in increasing nozzle density in the printhead.
In an effort to solve the above problems, it is a feature of an embodiment of the present invention to provide an ink-jet printhead in which a nozzle, an ink chamber, and an ink feed hole are formed in one channel thereby minimizing an area per unit nozzle and increasing a nozzle density.
Accordingly, the present invention provides an ink-jet printhead including: a nozzle plate having a nozzle for ejecting ink; a substrate having an ink feed hole for supplying ink from an ink reservoir, the substrate being separated from the nozzle plate by a predetermined distance; and an intermediate layer interposed between the substrate and the nozzle plate, the intermediate layer including an ink chamber connected to the ink feed hole and the nozzle and a heating element surrounding the ink chamber. Preferably, the nozzle, the ink chamber, the ink feed hole are formed in a straight channel.
The heating element includes a first heater for generating heat by the application of current, a second heater for receiving the heat generated by the first heater and boiling ink within the ink chamber to generate a bubble, and a heat transfer layer in contact with the first and second heaters for transferring the heat generated by the first heater to the second heater. Preferably, the second heater is formed of diamond, gold, copper, or silicon. Also preferably, the heat transfer layer is formed of either of diamond or SiC.
Preferably, the first heater, the heat transfer layer, and the second heater, excluding a portion in contact with the ink filling the ink chamber, are surrounded by an adiabatic layer. Also preferably, the adiabatic layer is formed of a silicon oxide layer.
Preferably, the heating element includes a first heater for generating heat by the application of current and a second heater for receiving the heat generated by the first heater and boiling ink within the ink chamber to generate a bubble. Also preferably, the second heater is formed of either diamond or SiC. Preferably, the first and second heaters, excluding a portion in contact with the ink filling the ink chamber, are surrounded by an adiabatic layer.